The concept of growing grass sod over a solid or impermeable base such as concrete or plastic sheeting goes back, as far as I know, to experiments conducted by the O. M. Scott Co. in Marysville, Ohio, starting in the summer of 1965. Bluegrass sod was grown over concrete on the front yard of the publisher of the local newspaper. It was grown successfully this way for several years, widely publicized, and used in O. M. Scott Co. advertising.
I started experimenting with and expanding the concept shortly thereafter at nearby Ohio Wesleyan University and demonstrated very shortly that it had several attractive features and advantages compared to the conventional system of growing sod on soil. First, and probably foremost, my research indicated that if grass seed was germinated in a suitable medium placed over a solid or impermeable base, typically 1-6 mil polyethylene sheeting or film, and given optimum growing conditions, the turfgrasses would begin to grow in such a manner that the primary rooting system of the grasses would quickly bind the growing medium into a sod. The sod, complete with the young rooting system, could be peeled or rolled intact and coherent after only a few weeks off the plastic sheeting or impermeable base. Various types of nettings could also be inserted into the growing medium which, as in conventional sodding, enhanced even further the speed with which the sod would be ready to harvest.
The quick formation of the sod was an obvious advantage over the conventional system of producing sod on soil in which 1-2 years or even more are required before the sod is knitted sufficiently to remain coherent when harvested with a sod cutter.
Conventional sod on soil requires the formation of rhizomes, tillers, secondary roots, and stolons, and the intertwining of these growth processes which take a relatively lengthy amount of time to bind the grasses and soil into a sod. The extensive primary rooting system is essentially lost in conventional sod production since it goes deep into the soil and is of little or no consequence in the binding of the sod.
On the other hand by germinating the seed over a solid base such as plastic sheeting the primary rooting of the seedlings is trapped, so to speak; and since the primary rooting is quite extensive (one rye seedling has been reputed to produce 17 miles of roots) it runs along the solid base through the growing medium and quickly binds it into a sod in a matter of a few weeks.
The feature of using the primary rooting system of grasses to speed the formation of sod seemed at the time useful and valid, and I incorporated the research into a patent disclosure (#012097) in July of 1972 followed a year later by a patent application (Ser. No. 371,462). During the time, however, that the patent was being reviewed it became apparent that the methods did not translate well into the large scale type production demanded by the U.S. sod industry. I could not make the transition from the greenhouse bench, laboratory, or small plot to a field scale production. I subsequently abandoned the patent application as being premature, but I did publish my observations in the trade magazine, Weeds, Trees, and Turf. The methods as they existed at that time were simply not cost effective in competition with the U.S. sod industry which by the 1970's had become large in scale, efficient, and highly mechanized.
Other workers in Great Britain such as Goodall, Dawson, and Loads, faced similar difficulties and also the disadvantage that they were not familiar with the U.S. sod industry. All of their processes failed the test of practicality and cost effectiveness. As a result none of these inventions became commercially significant in the U.S. because of inherent problems that at the time were difficult or even impossible to solve. The problems are discussed below:
First, and probably the main problem, has been the availability of an inexpensive, yet plentiful growing medium. Hundreds of things appear to work in a greenhouse or small plot until one considers the weight, cost availability, ease of handling, trucking, spreading, and the expense to bring the growing medium up to nutritional minimums.
Second, the amount of growing material required to cover an acre sheet of plastic one inch deep translates into 134 cubic yards or over 20 single axle dump truck loads per acre! Quantities of rooting material of this dimension, their handling and manipulation, are obviously too expensive to be competitive with the conventional sod on soil process.
Third, placing an exact amount of growing material (such as one-fourth inch as proposed by Loads) evenly over acres of plastic film proved very difficult. While it worked "indoors" under controlled conditions in a greenhouse flat, it could not be readily obtained on a field scale. Furthermore, one-fourth inch of material outdoors was an insufficient amount of rooting material under the best conditions. Even one inch of material was not successful: it could not be spread or maintained evenly. A slight thunderstorm of the type prevalent in the Midwest would sheet erode the growing medium, washing it off the plastic film or other base, causing gaps that prevented continuous rooting and hence sod formation.
Fourth, some provision had to be made to eliminate or at least reduce the effect of thunderstorms or heavy rains on the early stages of the sod development. Any upsetting of the thin patina of growing material over the base produced gaps and distortions that prevented continuous rooting and hence sod formation.
Fifth, another important consideration is damping-off disease. Since the primary rooting of the seeding will functionally knit the sod (rather than the secondary rooting, rhizomes, stolons, tillers of conventional sod), the seeding rate is increased which in turn increases the incidence of damping-off. This devastating disease is expensive, often impossible, to control with fungicides.
Sixth, the use of foams, of containers as proposed by Dawson, or of curbs as proposed by Loads, or of burlap as proposed by Goodall, or of rolling up the plastic film to transport the grass as in Blackburn were all too expensive to be considered. The process had no validity whatsoever unless the plastic film could be used over and over again.
And finally seventh, conventional sodding is very labor intensive. Significantly reducing the amount of hard labor involved has to be a prime attribute of any alternative sodding system.
These major problems, then, had to be solved before any alternative sodding system could literally get off the ground. Starting in the 1982 season several things began to make an alternative sodding system more feasible. In essence it became possible to solve the problems.
First, around the country the Beltsville system of composting sewage sludge has begun to catch on. Suddenly, at least in Central Ohio, there is a readily available source of growing materials which in large quantities is being offered at an attractive price. This "Comtil", as is it called in Columbus, Ohio, was quickly determined to support the growth of turfgrasses without amendment. It was not only charged naturally with the right nutrients for grass culture, but it was also established that it retarded the development of damping-off and other fungal diseases! Problems No. 1 and 5 above then were solved in one step.
Next I made the important discovery that wheat straw could be used not only to protect the solid base from truck and tractor traffic but also to keep the growing medium in place in a thunderstorm. Furthermore, in the right condition, I discovered that the straw actually substituted for additional growing media, that is conferred some unidentified biological property in the mix that encouraged the growth of turfgrasses. Thus, the straw made it possible to drastically reduce the amount of expensive growing medium required to effect a sod. In addition it eliminated the problem of having to spread the medium on a solid base with a uniform thickness that was impossible to obtain. These new uses for straw were the most important discoveries made and effectively solved Problems No. 2, 3, and 4.
Another recent important development in the turf industry has made an alternative sod more feasible: this is the introduction of turf-type tall or coarse fescues. These new turf cultivars have several advantages over bluegrass: They are more drought, insect, and disease resistant. They are more durable on playing fields, and they germinate and root more quickly, more vigorously than bluegrass. On the other hand the tall fescues do not produce rhizomes and stolons and hence do not lend themselves to conventional sod production. In practice these drawbacks are compensated for by growing the sod for a longer than usual period, by laying sod netting, and by adding bluegrass to the tall fescue seeding. The netting, however, is expensive and difficult to use, and the bluegrass in time is much more aggressive than the tall fescue. Eventually it takes over the turf with the new lawn becoming heterogeneous and the tall fescue scattering into unsightly clumps.
These apparent disadvantages to growing a tall fescue sod in a conventional manner turn out to be strengths when tall fescue is considered as the main ingredient of an alternative sod grown on a solid base. The vigorous and rapid primary rooting gives the tall fescue cultivars a distinct advantage over the less vigorous bluegrass.
The tall fescue cultivars have one more subtle but very important advantage over other turfgrasses which I will explain: In the past it has been impossible to find wheat straw that was totally free of unharvested wheat seed. In the production of an alternative bluegrass sod this wheat seed would germinate much more quickly than bluegrass, obscure it, and retard its development. As well, wheat seedlings are much more coarse than fine turf premium bluegrasses and do not readily mow out; and then the new sod quickly becomes ragged, unattractive, and in fact unsaleable.
When tall fescue turf is grown, however, the wheat seed germinates at about the same speed. Furthermore the width and coarseness of the wheat blades is more comparable to that of the tall fescue when mowed close, and hence the new turf looks more uniform. As well the wheat also has a vigorous primary rooting system which aids the rapid development of the sod. Initially at least the annual wheat withstands close mowing even to an inch or less and acts in fact as a beautiful nurse crop.
Another advantage to the tall fescue/wheat seeding is that it germinates quickly, in a matter of days, and hence lends to the new sod a more rapid resistance to thunderstorms than when bluegrass constitutes the primary seeding.
Technically speaking, it is important to my alternative system to start not just with wheat "straw" but in fact with the whole culm including the inflorescence. Even a rotary combine will leave enough mature caryopses in the spikelets to benefit the early formation of the alternative tall fescue sod. No longer objectionable, the unharvested wheat seed is now desirable.
In summary, then, the tall fescue/wheat seeding germinates much more quickly than bluegrass; its coarse texture is homogeneous and not unattractive; and coupled with quick germination is a very rapid, extensive primary root growth. I have discovered that this tall fescue/wheat primary root growth is so vigorous that nettings, gels, absorbents, or any supplemental bluegrass seed is obviated. Furthermore, the new sod can be produced in much less time, at considerable savings in weight, than conventional tall fescue sod on soil.
The whole culms are spread about two inches deep over the solid base and now only 30-40 cubic yards of growing material/acre are required. This is spread over the straw and seeded conventionally. The rooting material fills the voids and interstices of the straw making a coherent, thunderstorm resistant, germinating matrix.
I discovered that in a few weeks the initial two inches of straw will compress and decompose into a mat or sod approximately one-half inch thick. The binding quality of the straw plus the external primary rooting system of the grasses combine to make a bona fide sod of high quality.
Harvesting the alternative sod has a distinct advantage over conventional sodding techniques. The sod is rolled up off the plastic base with the primary rooting intact rather than being cut off the soil by a sod cutter. Since it is slightly lighter and more tightly bound, it is possible to produce the sod in rolls much larger than conventional sod harvested by a Ryan or Brouwer sod cutter--even as wide as a truck bed with each roll comprised of 20-50 square yards. The rolls are loaded directly; no pallet is required. At the laying site the rolls are unloaded and installed by the grader and the raker obviating both a fork lift and a laying crew. This is a significant reduction in labor.
The solid base alternative sodding system is now competitive.